Abstract

The nature of dark matter remains a key question in astrophysics, since the current Lambda Cold Dark Matter (ΛCDM) paradigm exhibits a number of discrepancies between predictions of structure on sub-galactic scales and observations. An alternative to CDM is Warm Dark Matter (WDM) consisting of O(keV) particles. In WDM, small scale structure is suppressed resulting in a dearth of low mass M h < 10^9 Msol halos. As galaxies residing in low mass halos are effective at polluting the intergalactic medium (IGM) with metals, one naturally expects less metals in the IGM in WDM compared to CDM. Therefore we study the impact of WDM on the metal enrichment of the IGM. In this work we focus on WDM consisting of 1.5 keV particles, as it is this cosmology that harbors a significant dearth of low mass halos. To do this,
we use a semi-analytical model in which we explore several feedback scenarios consisting of internal (supernova) and external (ultraviolet) feedback. In both CDM and 1.5 keV WDM, the effect of feedback on the Ultra Violet luminosity function, stellar mass density, ejected gas
mass density and eventually on the cosmological mass density of C IV in the IGM is explored. We find the metal enrichment of the IGM in 1.5 keV WDM to be delayed and accelerated with respect to CDM. In addition, we note that the effect of baryonic feedback in CDM is degenerate with the effect of WDM. Observed C IV densities are only reproduced in the case of CDM without
any external feedback, and therefore within the caveats of this model, we can rule out 1.5 keV WDM and all CDM scenarios except the fiducial one.